Add accept methods to handler sets.

CHANGELOG.md

@@ -9,6 +9,12 @@ The format is based on [Keep a Changelog], and this project adheres to
 [Keep a Changelog]: https://keepachangelog.com/en/1.0.0/
 [Semantic Versioning]: https://semver.org/spec/v2.0.0.html
 
+## [Unreleased]
+
+### Added
+
+- Add `HandlerSet.AcceptVisitor()` and `RichHandlerSet.AcceptRichVisitor()`
+
 ## [0.1.0] - 2019-12-02
 
 - Initial release

fixtures/visitor.go

@@ -25,13 +25,7 @@ func (v *Visitor) VisitApplication(ctx context.Context, cfg configkit.Applicatio
 		return v.VisitApplicationFunc(ctx, cfg)
 	}
 
-	for _, h := range cfg.Handlers() {
-		if err := h.AcceptVisitor(ctx, v); err != nil {
-			return err
-		}
-	}
-
-	return nil
+	return cfg.Handlers().AcceptVisitor(ctx, v)
 }
 
 // VisitAggregate calls v.VisitAggregateFunc(ctx, cfg) if it is non-nil.
@@ -89,13 +83,7 @@ func (v *RichVisitor) VisitRichApplication(ctx context.Context, cfg configkit.Ri
 		return v.VisitRichApplicationFunc(ctx, cfg)
 	}
 
-	for _, h := range cfg.RichHandlers() {
-		if err := h.AcceptRichVisitor(ctx, v); err != nil {
-			return err
-		}
-	}
-
-	return nil
+	return cfg.RichHandlers().AcceptRichVisitor(ctx, v)
 }
 
 // VisitRichAggregate calls v.VisitAggregateFunc(ctx, cfg) if it is non-nil.

handlerset.go

@@ -1,6 +1,10 @@
 package configkit
 
-import "github.com/dogmatiq/configkit/message"
+import (
+	"context"
+
+	"github.com/dogmatiq/configkit/message"
+)
 
 // HandlerSet is a collection of handlers.
 type HandlerSet map[Identity]Handler
@@ -111,6 +115,22 @@ func (s HandlerSet) Filter(fn func(Handler) bool) HandlerSet {
 	return subset
 }
 
+// AcceptVisitor visits each handler in the set.
+//
+// It returns the error returned by the first handler to return a non-nil error.
+// It returns nil if all handlers accept the visitor without failure.
+//
+// The order in which handlers are visited is not guaranteed.
+func (s HandlerSet) AcceptVisitor(ctx context.Context, v Visitor) error {
+	for _, h := range s {
+		if err := h.AcceptVisitor(ctx, v); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // RichHandlerSet is a collection of rich handlers.
 type RichHandlerSet map[Identity]RichHandler
 
@@ -245,3 +265,19 @@ func (s RichHandlerSet) Filter(fn func(RichHandler) bool) RichHandlerSet {
 
 	return subset
 }
+
+// AcceptRichVisitor visits each handler in the set.
+//
+// It returns the error returned by the first handler to return a non-nil error.
+// It returns nil if all handlers accept the visitor without failure.
+//
+// The order in which handlers are visited is not guaranteed.
+func (s RichHandlerSet) AcceptRichVisitor(ctx context.Context, v RichVisitor) error {
+	for _, h := range s {
+		if err := h.AcceptRichVisitor(ctx, v); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

handlerset_test.go

@@ -1,6 +1,9 @@
 package configkit_test
 
 import (
+	"context"
+	"errors"
+
 	. "github.com/dogmatiq/configkit"
 	cfixtures "github.com/dogmatiq/configkit/fixtures"
 	"github.com/dogmatiq/dogma"
@@ -208,6 +211,49 @@ var _ = Describe("type HandlerSet", func() {
 			Expect(set.Has(projection)).To(BeTrue())
 		})
 	})
+
+	Describe("func AcceptVisitor()", func() {
+		BeforeEach(func() {
+			set.Add(aggregate)
+			set.Add(projection)
+		})
+
+		It("visits each handler in the set", func() {
+			var visited []Handler
+
+			err := set.AcceptVisitor(
+				context.Background(),
+				&cfixtures.Visitor{
+					VisitAggregateFunc: func(_ context.Context, cfg Aggregate) error {
+						Expect(cfg).To(BeIdenticalTo(aggregate))
+						visited = append(visited, cfg)
+						return nil
+					},
+					VisitProjectionFunc: func(_ context.Context, cfg Projection) error {
+						Expect(cfg).To(BeIdenticalTo(projection))
+						visited = append(visited, cfg)
+						return nil
+					},
+				},
+			)
+
+			Expect(err).ShouldNot(HaveOccurred())
+			Expect(visited).To(ConsistOf(aggregate, projection))
+		})
+
+		It("returns an error if one of the handlers fails", func() {
+			err := set.AcceptVisitor(
+				context.Background(),
+				&cfixtures.Visitor{
+					VisitProjectionFunc: func(_ context.Context, cfg Projection) error {
+						return errors.New("<error>")
+					},
+				},
+			)
+
+			Expect(err).To(MatchError("<error>"))
+		})
+	})
 })
 
 var _ = Describe("type RichHandlerSet", func() {
@@ -409,4 +455,47 @@ var _ = Describe("type RichHandlerSet", func() {
 			Expect(set.Has(projection)).To(BeTrue())
 		})
 	})
+
+	Describe("func AcceptRichVisitor()", func() {
+		BeforeEach(func() {
+			set.Add(aggregate)
+			set.Add(projection)
+		})
+
+		It("visits each handler in the set", func() {
+			var visited []RichHandler
+
+			err := set.AcceptRichVisitor(
+				context.Background(),
+				&cfixtures.RichVisitor{
+					VisitRichAggregateFunc: func(_ context.Context, cfg RichAggregate) error {
+						Expect(cfg).To(BeIdenticalTo(aggregate))
+						visited = append(visited, cfg)
+						return nil
+					},
+					VisitRichProjectionFunc: func(_ context.Context, cfg RichProjection) error {
+						Expect(cfg).To(BeIdenticalTo(projection))
+						visited = append(visited, cfg)
+						return nil
+					},
+				},
+			)
+
+			Expect(err).ShouldNot(HaveOccurred())
+			Expect(visited).To(ConsistOf(aggregate, projection))
+		})
+
+		It("returns an error if one of the handlers fails", func() {
+			err := set.AcceptRichVisitor(
+				context.Background(),
+				&cfixtures.RichVisitor{
+					VisitRichProjectionFunc: func(_ context.Context, cfg RichProjection) error {
+						return errors.New("<error>")
+					},
+				},
+			)
+
+			Expect(err).To(MatchError("<error>"))
+		})
+	})
 })